Types of Threaded Fasteners

 Used to hold parts together  Clearance holes in parts  Nut on other end  Can also be used with a threaded hole

 Used for assembly of machine parts  Coarse & fine threads  Diameters from.06 to.50  Lengths from.125 to 3  Several head sizes available

 Fine finished machine screws  Generally threaded into a tapped hole  Diameters from.06 to 4  Variety of head types

 Used to clamp parts on a shaft (pulleys, gears)  Ensure that the part stays on the shaft and rotates with it  can have several drive types  Variety of point types for different applications

 Have a mechanism to keep them attached to a panel when unthreaded  Keeps the screw from being lost when the panel is removed  Makes it easier to reinstall the panel  Developed by the military

 2 types of holes Thru holes-go thru the part Blind holes-don’t go thru  Thru holes are easier to perform tapping operation (cut chips can fall out other side)  Blind holes require special design  Hole has to be made deeper than the threads will go

 Must be designed with allowance for incomplete threads from tool runout  External threads should have a lead in chamfer Tool Runout-distance the tool can go beyond the required full thread length

 Have a special locking mechanism in it  Can be a plug or ring of soft metal or plastic  Spins freely until locking mechanism is engaged

 Thin nut used with a standard nut  Friction between them locks them into place  Not used much (older practice)

 Slots around the top of the nut to accept a cotter pin  Pin goes through a hole in the fastener

 Designed to attach things to wood  Pilot hole must be drilled first

 Cut their own threads in a hole  No tapping operation required  Used in variety of materials from plastic to metal  Special design at the bottom of the thread does the cutting  Some can also drill hole (thin material)

 Helically formed coils of diamond shape wire  Inserted into a threaded hole  Used to repair damaged or worn out threaded holes

o Some are used to provide stronger threaded hole in softer material

 Usually only shown on assembly drawings  Hex shapes drawn across corners  Fasteners should be drawn all in same orientation  Slotted fasteners should be drawn with drive feature horizontal  Fasteners are not sectioned in section views

Uses for washers:  Span oversized holes  Distribute loads over a larger area  Locking device  seal

 Plain flat shape  Span oversized holes  Made from many materials

 Trapezoidal wire formed in a helix (looks like one coil of a spring)  Free height is about 2X the thickness  Used as a locking device  Spring pressure increases the friction between mating threads

 Has teeth that dig into the face of the part and the head of the fastener to keep it from loosening  Made from hardened carbon steel

 Molded or stamped nonmetallic washers  Available in many materials  Used as:  Protect surface of a part  Electrical insulator  Seals

Terminology:  Pitch  Lead  Thread form  Tap drill  Die  Self tapping screw  Set screw  3 types of thread representation (which one is common)  Thread notes (metric & inch)  How to note left handed  Thread classes (metric & inch) (what they control and the types)  3 basic locking methods  2 functions of washers